Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data. In general, the wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit (Tx) power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc.
As disclosed in section 6 of 3rd generation partnership project (3GPP) partnership project) TS 36.211 V8.0.0 (2007-09) “Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 8)”, a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), a physical hybrid ARQ indicator channel (PHICH), etc., are examples of downlink control channels used in 3GPP long term evolution (LTE). The PCFICH is transmitted at a first orthogonal frequency division multiplexing (OFDM) symbol of a subframe and carries information regarding the number of OFDM symbols used to transmit control channels within the subframe. Control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI includes uplink or downlink scheduling information or includes an uplink Tx power control command for arbitrary user equipment (UE) groups. The PHICH carries an acknowledgement (ACK)/not-acknowledgement (NACK) signal for hybrid automatic repeat request (HARM).
In the 3GPP LTE, the downlink control channels are allocated to a limited region called a control region in a subframe. However, since the PDCCH is allocated to a resource region in which a resource region used by the PCFICH and the PHICH is excluded, a UE has to know the resource region used by the PCFICH and the PHICH in order for the UE to receive the DCI transmitted on the PDCCH. Since the PCFICH uses a pre-fixed resource region in the 3GPP LTE, a base station (BS) needs to report the resource region used by the PHICH to the UE.
In section 7.4 of 3GPP TS 36.300 V8.3.0 (2007-12), system information is divided into master information block (MIB) and a number of system information blocks (SIBs). The MIB defines the most essential physical layer information of the cell required to receive further system information. SIB Type 1 which is referred to as SIB-1 contains information relevant when evaluating if a UE is allowed to access a cell and defines the scheduling of other system information blocks. The Physical Broadcast Channel (PBCH) carries the MIB.
Korean Patent Application No. 2008-0079740, entitled “METHOD FOR ACQUIRING RESOURCE REGION INFORMATION FOR PHICH AND METHOD OF RECEIVING PDCCH” filed on Aug. 14, 2008 by this applicant, discloses a technique to acquire resource region for a PHICH by using the MIB on PBCH. The MIB may include a PHICH duration in a subframe and/or the number of PHICH per subframe. The resource region may be acquired based on the information in the MIB.
The MIB on PBCH uses a fixed scheduling and includes a limited number of essential and most frequently transmitted parameters that are needed to acquire other information from the cell. If the resource region of the PHICH is invariant every subframe, it may be efficient to acquire the resource region of the PHICH based on the information in the MIB.
If the resource region used by the PHICH can vary in every subframe, a control region assigned with the control channels can be more flexibly allocated. In particular, the control region needs to be allocated more flexibly in a time division duplex (TDD) system of which the number of downlink subframes included in one radio frame is less than that of a frequency division duplex (FDD) system. However, an amount of information regarding the resource region used by the PHICH is too large to transmit the information in every subframe.
Accordingly, there is a need for a method of more flexibly allocating resources of a PHICH.